At least 14 people were wounded in an apparent mass stabbing at Lone Star College's CyFair campus in Cypress, Texas, on Tuesday morning.
The suspect, a white male armed with what one witness described as an X-Acto knife, was detained, police said. The suspect, believed to be 21, was enrolled at the school.
Harris County Sheriff Adrian Garcia said police received a 911 call at 11:12 a.m. local time reporting a white male "on the loose stabbing people."
The school was placed on lockdown.
"Seek shelter now," Lone Star College's Twitter feed warned Tuesday afternoon. "If away, stay away."
The incident occurred near and around the school's Health Science Center and remains an active crime scene, Garcia said.
"Buildings are still being searched," he added.
Four victims were transported by helicopter with serious injuries "consistent with laceration," a spokesman for the Harris County Sheriff's Office said. Two others were taken by ambulance to a local trauma center.
Two of those victims are in critical condition, he said. Four are in fair condition. Others victims were treated for minor injuries, and two refused treatment, Garcia said.
One witness told CNN that the stabber was hearing impaired.
An announcement was made over loudspeakers warning students to seek shelter. "This is an emergency," the announcement said, according to KHOU-TV. "Everybody stay inside of your rooms. Do not leave your rooms."
An alert issued on the school's website indicated that "another suspect may possibly be at large." But Garcia said surveillance video reviewed by police indicated there was one "and only one" suspect.
An Instagram user who said he helped apprehend the stabber posted a photo of a man face down on the ground with a backpack. He said the man had stabbed five people, including two girls in the cheek. "Everyone ran the other way ... ," he said. "Me and this kid got em." #copsaretooslow
Police would not confirm the exact weapon used, but said no firearms were found at the scene.
The campus was evacuated, Vice Chancellor Randy Key told reporters, and the college will remain closed for the remainder of the day.
In January, three people were wounded in a shooting at Lone Star College's North Harris campus near Houston. More than 90,000 students attend classes across the Lone Star College system's six campuses.